The design, fabrication, and characterization of a resonant cavity-enhanced photodetector (RCE PD) operating in the long-wavelength infrared regime are demonstrated. The incorporation of the low bandgap InAs/InAs0:70Sb0:30 type-II strained-layer superlattice into the absorber layer of the detector cavity, along with the high-reflectivity (Rm > 0.9) AlAs0:08Sb0:92/GaSb distributed Bragg reflector pairs, results in resonant enhancement at 7.7–7.8 lm, which is a spectral region relevant in applications in sensing of chemical warfare agents and in medical biomarker diagnostics. These resonant wavelength peaks also display a high quality factor in the range of 76–86 and a small temperature coefficient of 0.52 nm K1. An nBn architecture, where an Al0:71Ga0:29As0:08Sb0:92 layer acts as a barrier for majority electrons while minimizing the valence band offset with the absorber, is also incorporated into the cavity in order to improve the electrical properties of the detector. Spectral response measurements yield a peak external quantum efficiency of 14.6% and a peak responsivity of 0.91 A W1 at 77 K and 0.8 V; meanwhile, a dark current density of 2.0 104 A cm2 at 77 K results in a specific detectivity of 3.7 1010 cm Hz1=2 W1, coming close to the theoretical background-limited D of an ideal broadband photovoltaic detector with the superlattice composition as that of the RCE PD.